The facile synthesis of nanometer-length scales as well as control over the dimensions of inorganic and organic material nanostructures is essential due to their unique size-dependent properties and promising potential applications in nanodevices, such as field-effect transistors,[1] sensor/actuator arrays,[2] optoelectronic devices,[3] and in biotechnology[4] (e.g., delivery agents for pharmaceutical agents) as well as catalytic and analytical systems.[5] Conducting polymers are a unique class of organic materials and are emerging as a promising material for synthesis of nanostructured materials and devices due to their electrical, electronic, magnetic, and optical properties.[6]Conducting polymers offer great prospect for practical applications[6, 7] which range from chemical and biological sensing and diagnosis to energy conversion and storage, light-emitting display devices, catalysis, drug delivery, separation, microelectronics, and optical storage due to their unparalleled architectural diversity and flexibility, low cost, and ease of synthesis. In recent years, conducting polymer-based[8] nanostructured materials in the shape of thin films and nanowires have attracted much attention for the construction of fast, inexpensive, and dimensionally appropriate devices.c[9]
Among all conducting polymers, polyaniline (PANi) is probably the most widely studied because it has a broad range of tunable properties derived from its structural flexibility. The doping level of PANi can be readily controlled through an acid/base dedoping process,[10] and it has high conductivity, good environmental stability and easy preparation. Different morphologies of PANi have been obtained through different synthesis or processing routes.[11] Low-dimensional nanostructures of PANi in various shapes and forms, for example, nanoparticles, nanowires, nanofibers, nanoshells, and nanotubes, have been produced.[12] Conducting PANi nanostructures are prime candidates for replacing conventional bulk materials in micro- and nanoelectronic devices[13] and in chemical[14] and biological[15,16] sensors, because they combine the properties of low-dimensional organic conductors with high surface area materials. Also, PANi nanostructures have metal-like and controllable conductivity as well as both thermal and environmental stability.
Synthesis of PANi one-dimensional (1-D) nanostructures has been carried out both chemically and electrochemically by polymerizing the aniline using templates,[16-18] surfactants,[19,20] liquid crystals,[21] thiolated cyclodextrins,[22] polyacids,[23] electrospinning,[24] mechanical stretching,[25] coagulating media,[26] interfacial polymerization,[12,14] seeding[27] and dilute polymerization. [28] Despite all of the progress in nanostructure synthesis, PANi's limitation in processibility continues to prevent it from fully reaching its practical potential. Especially for devices with features increasingly reducing in size, there is a pressing need for a practical method capable of reproducibly integrating PANi onto selected device structures with precision and control. Recently, Semancik et al.[13] demonstrated that PANi colloidal suspensions have excellent processability when applied electrophoretically.
Dispersion of this polymer is another interesting way to improve processability. Aqueous dispersions of PANi have been studied by many research groups using stabilizer surfactant,[29] and by controlling pH.[30]However, PANi nanostructure processability in common solvents is yet to be accomplished.
Aromatic boronic acids are known to bind compounds containing diol moieties such as carbohydrates, vitamins, coenzymes and ribonucleic acids with high affinity through reversible ester formation.[31] A similar reaction was used to achieve chemical[32] and electrochemical[33] polymerization of self-doped poly(anilineboronic acid) (PABA) through formation of an anionic boronic ester complex between 3-aminophenylboronic acid and D-fructose in the presence of fluoride. The equilibrium reaction of boronic acid with fluoride is also known to produce a tetrahedral anionic complex.[34] This is the source of fluoride-catalyzed polymerization of 3-aminophenylboronic acid under acidic conditions.[35] Fabre and co-workers[35] suggested that in the presence of fluoride, PABA is a self-doped polymer under acidic conditions. Similarly, aromatic boronic acids reversibly complex with aliphatic alcohols, the equilibrium constant for boronic acid-alcohol complex decreasing with increasing steric size of the alcohol i.e., methanol>ethanol>1-propanol.[36]